Change order approval based on Payment terms change and Requestor change in BPM

Business needs to trigger change orders if the payment terms or Requestor is changed on the PO by change orders. if not there is no approval needed.

I found and tried these parameters with no success:

PurchasingDocumentHeader.isChangeOrder is "Y" and

PurchasingDocumentDistribution.requesterOnPoModified is "Y" or

PurchasingDocumentHeader.paymentTermsModified is "Y"

Has anybody had the same request?, how was it solved?

Thank you in advance.